BAEL-6438 Code for the Find the longest word in a given string article

core-java-modules/core-java-string-operations-5/src/main/java/com/baeldung/longestword/LongestWordFinder.java

@@ -0,0 +1,36 @@
+package com.baeldung.longestword;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Optional;
+import java.util.stream.Collectors;
+
+public class LongestWordFinder {
+
+    public Optional<String> findLongestWord(String sentence) {
+        return Optional.ofNullable(sentence)
+          .filter(string -> !string.trim()
+            .isEmpty())
+          .map(string -> string.split("\\s"))
+          .map(Arrays::asList)
+          .map(list -> Collections.max(list, Comparator.comparingInt(String::length)));
+    }
+
+    public List<String> findLongestWords(String sentence) {
+        if (sentence == null || sentence.trim()
+          .isEmpty()) {
+            return Collections.emptyList();
+        }
+        String[] words = sentence.split("\\s");
+        int maxWordLength = Arrays.stream(words)
+          .mapToInt(String::length)
+          .max()
+          .orElseThrow();
+        return Arrays.stream(words)
+          .filter(word -> word.length() == maxWordLength)
+          .collect(Collectors.toList());
+    }
+
+}

core-java-modules/core-java-string-operations-5/src/test/java/com/baeldung/longestword/LongestWordFinderUnitTest.java

@@ -0,0 +1,62 @@
+package com.baeldung.longestword;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+class LongestWordFinderUnitTest {
+
+    LongestWordFinder longestWordFinder = new LongestWordFinder();
+
+    @Test
+    void givenNull_whenFindLongestWord_thenEmpty() {
+        assertThat(longestWordFinder.findLongestWord(null)).isEmpty();
+    }
+
+    @Test
+    void givenEmptyString_whenFindLongestWord_thenEmpty() {
+        assertThat(longestWordFinder.findLongestWord("")).isEmpty();
+    }
+
+    @Test
+    void givenStringWithOnlySpaces_whenFindLongestWord_thenEmpty() {
+        assertThat(longestWordFinder.findLongestWord("   ")).isEmpty();
+    }
+
+    @Test
+    void givenAPhraseWithALongestWord_whenFindLongestWord_thenLongestWordOfThePhrase() {
+        assertThat(longestWordFinder.findLongestWord("This is a phrase with words")).hasValue("phrase");
+    }
+
+    @Test
+    void givenAPhraseWithVariousWordsOfMaxLength_whenFindLongestWord_thenAnyOfTheLongestsWordsOfThePhrase() {
+        assertThat(longestWordFinder.findLongestWord("Baeldung is another word of size eight in this sentence")
+          .get()).isIn("Baeldung", "sentence");
+    }
+
+    @Test
+    void givenNull_whenFindLongestWords_thenEmpty() {
+        assertThat(longestWordFinder.findLongestWords(null)).isEmpty();
+    }
+
+    @Test
+    void givenEmptyString_whenFindLongestWords_thenEmpty() {
+        assertThat(longestWordFinder.findLongestWords("")).isEmpty();
+    }
+
+    @Test
+    void givenStringWithOnlySpaces_whenFindLongestWords_thenEmpty() {
+        assertThat(longestWordFinder.findLongestWords("   ")).isEmpty();
+    }
+
+    @Test
+    void givenAPhraseWithALongestWord_whenFindLongestWords_thenLongestWordOfThePhrase() {
+        assertThat(longestWordFinder.findLongestWords("This is a phrase with words")).containsExactly("phrase");
+    }
+
+    @Test
+    void givenAPhraseWithVariousWordsOfMaxLength_whenFindLongestWords_thenAllLongestsWords() {
+        assertThat(longestWordFinder.findLongestWords("Baeldung is another word of size eight in this sentence")).containsExactly("Baeldung", "sentence");
+    }
+
+}